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英['lɪs(ə)n] 美['lɪsn]
vi. 听,倾听;听从,听信
n. 听,倾听

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草莓小菇凉:说的非常好,十分有道理,棒棒棒!

06-08 15:44:55

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TPO-01-Groundwater

Groundwater is the word used to describe water that saturates the ground, filling all the available spaces. By far the most abundant type of groundwater is meteoric water; this is the groundwater that circulates as part of the water cycle. Ordinary meteoric water is water that has soaked into the ground from the surface, from precipitation (rain and snow) and from lakes and streams. There it remains, sometimes for long periods, before emerging at the surface again. At first thought it seems incredible that there can be enough space in the "solid" ground underfoot to hold all this water. 


The necessary space is there, however, in many forms. The commonest spaces are those among the particles—sand grains and tiny pebbles—of loose, unconsolidated sand and gravel. Beds of this material, out of sight beneath the soil, are common. They are found wherever fast rivers carrying loads of coarse sediment once flowed. For example, as the great ice sheets that covered North America during the last ice age steadily melted away, huge volumes of water flowed from them. The water was always laden with pebbles, gravel, and sand, known as glacial outwash, that was deposited as the flow slowed down. 

The same thing happens to this day, though on a smaller scale, wherever a sediment-laden river or stream emerges from a mountain valley onto relatively flat land, dropping its load as the current slows: the water usually spreads out fanwise, depositing the sediment in the form of a smooth, fan-shaped slope. Sediments are also dropped where a river slows on entering a lake or the sea, the deposited sediments are on a lake floor or the seafloor at first, but will be located inland at some future date, when the sea level falls or the land rises; such beds are sometimes thousands of meters thick.

In lowland country almost any spot on the ground may overlie what was once the bed of a river that has since become buried by soil; if they are now below the water’s upper surface (the water table), the gravels and sands of the former riverbed, and its sandbars, will be saturated with groundwater. 

So much for unconsolidated sediments. Consolidated (or cemented) sediments, too, contain millions of minute water-holding pores. This is because the gaps among the original grains are often not totally plugged with cementing chemicals; also, parts of the original grains may become dissolved by percolating groundwater, either while consolidation is taking place or at any time afterwards. The result is that sandstone, for example, can be as porous as the loose sand from which it was formed.

Thus a proportion of the total volume of any sediment, loose or cemented, consists of empty space. Most crystalline rocks are much more solid; a common exception is basalt, a form of solidified volcanic lava, which is sometimes full of tiny bubbles that make it very porous.

The proportion of empty space in a rock is known as its porosity. But note that porosity is not the same as permeability, which measures the ease with which water can flow through a material; this depends on the sizes of the individual cavities and the crevices linking them.

Much of the water in a sample of water-saturated sediment or rock will drain from it if the sample is put in a suitable dry place. But some will remain, clinging to all solid surfaces. It is held there by the force of surface tension without which water would drain instantly from any wet surface, leaving it totally dry. The total volume of water in the saturated sample must therefore be thought of as consisting of water that can, and water that cannot, drain away. 

The relative amount of these two kinds of water varies greatly from one kind of rock or sediment to another, even though their porosities may be the same. What happens depends on pore size. If the pores are large, the water in them will exist as drops too heavy for surface tension to hold, and it will drain away; but if the pores are small enough, the water in them will exist as thin films, too light to overcome the force of surface tension holding them in place; then the water will be firmly held.

地下水是用来描述水饱和地面的词,填补所有可用的空间。到目前为止,最丰富的地下水类型是大气降水;这是作为水循环一部分循环的地下水。普通大气水是从地表,雨水和湖泊渗入地下的水。在那里,它仍然存在,有时是很长一段时间,再次出现在表面。起初以为在地下的“坚实”地面上有足够的空间容纳所有这些水似乎令人难以置信。

 

然而,这里有许多形式的必要空间。最常见的空间是沙粒和小卵石之间的松散,松散的沙子和沙砾。这种材料的床,在土壤下面看不见,是常见的。只要流过大量沉积物的快速河流都能找到它们。例如,在上个冰河时代覆盖北美的巨大冰盖逐渐融化,大量的水从它们流出。水中总是充斥着鹅卵石,砾石和沙子,被称为冰川外流,随着水流的减缓而沉积下来。

 

同样的事情发生在今天,尽管规模较小,无论是从一个山谷到一个相对平坦的土地上,出现一条含沙的河流或溪流,随着水流的减缓,其负荷也随之减小:水通常向外扩散,沉积沉积物以光滑的扇形斜坡的形式。河流进入湖泊或海洋时减速的沉积物也会下沉,沉积的沉积物首先在湖底或海底,但在海平面下降或陆地上升时将在未来某个时间位于内陆;这种床有时厚达数千米。

 

在低地国家,几乎任何地方的地方都可能覆盖曾经是被泥土掩埋的河床;如果它们现在在水面以下(地下水位),那么前河床和沙坝的沙砾和沙子将被地下水饱和。

 

非固结沉积物非常多。综合(或胶结)沉积物也含有数百万分钟的保水孔。这是因为原始颗粒之间的缝隙通常不会被固井化学物质完全堵塞;另外,在进行固结或之后的任何时间,部分原始颗粒可能会通过渗透地下水而溶解。其结果是,例如,砂岩可以像其形成的松散砂一样多孔。

 

因此,任何沉积物的总体积的一部分,松散的或胶结的,由空的空间组成。大多数结晶岩更坚硬;玄武岩是一种常见的例外,它是一种凝固的火山熔岩,有时充满了微小的气泡,使其非常多孔。

 

岩石中空隙的比例称为孔隙度。但要注意的是,孔隙度与渗透率不一样,渗透率是衡量水流过材料的容易程度;这取决于各个空腔的尺寸和连接它们的裂缝。

 

如果将样品放在合适的干燥地方,水饱和沉积物或岩石样品中的大部分水将从其中排出。但有些仍然会坚持所有坚实的表面。它被表面张力的力量保持在那里,水不会立即从任何潮湿的表面流失,完全干燥。因此,饱和样品中的总水量必须被认为是由水和不能排出的水组成。

 

这两种水的相对含量在不同的岩石或沉积物之间有很大的差异,尽管它们的孔隙度可能是相同的。发生什么事情取决于孔径大小。如果毛孔很大,那么它们中的水就会以重量过大的方式存在,不利于表面张力的保持,它会流失。但是如果孔隙足够小,那么它们中的水就会以薄膜形式存在,太轻以至于不能克服表面张力的作用力。那么水将被牢牢地抓住。

中文翻译

The phrase "So much for" in the passage is closest in meaning to

  • So much for unconsolidated sediments. Consolidated (or cemented) sediments, too, contain millions of minute water-holding pores.  A that is enough about B now let us turn to C of greater concern are D this is related to So much for
正确答案: A

网友解析

  • 用户头像

    十三个  发表于 2018-10-21 20:57:50

    so much for: 表面意思就是“已经很多了”,也就是足够的意思。A是足够;B是让我们转向;C是极受关注;D是这和…有关。根据词意,A是正确选项。对应原文So much for unconsolidated sediments. Consolidated (or cemented) sediments, too, contain millions of minute water-holding pores.代入原文,说unconsolidated未固结的沉积物已经说了很多了,下面就开始说固结的沉积物了,所以A正确,B和C都说我们马上要讨论的是未固结的沉积物,所以说反了;D表示与……相关,完全不沾边,错。

  • 用户头像

    joannazz  发表于 2017-12-04 15:31:22

    So much for 表示在这一部分就是这么多了,就不多说了,选A。

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